A radio frequency (RF) communication device may be subjected to fading phenomena which introduce distortion into a signal being received. These phenomena also increase the detrimental effect of additive noise on the received signal. One approach to overcoming the effects of fading is the use of a space diversity receiver system.
In a typical space diversity system, multiple receive antennas provide reception paths which are employed to receive a common source signal. Signal resolution hardware and software process the individual signals on the various reception paths, which are commonly referred to as diversity branches. The antennas are typically separated from one another by a great enough distance to guarantee that the received signals have been affected by uncorrelated fading a high proportion of the time. Thus, the probability that the received signals on all diversity branches are simultaneously experiencing deep fades is significantly less than the probability that any single received signal is experiencing a deep fade. With an appropriate combining algorithm, these received signals can be combined is such a way that the resultant signal is consistently of higher usability than is any of the individual, constituent signals.
A method well known in the art for combining these branch signals is called maximum ratio combining ("max-ratio"), see William C. Y. Lee, Mobile Communications Engineering, McGraw-Hill Book Company, New York, Copyright 1982. Using the max-ratio technique, the branch signals are adjusted so that they are in-phase, and then weighted in proportion to their individual signal amplitude to noise power ratios, before being combined via summation.
However, in practical implementations of max-ratio combining, delivered performance is degraded due to the presence of defects in the estimation of the signal amplitude to noise power ratios. Accordingly, a need arises for a method of max-ratio combining in a diversity system which does not substantially suffer from this problem.